The objective of this investigation is to study physiological and pathophysiological factors that affect the arteriovenous (a-v) and nutritive blood flow of the fingertps in normal subjects and patients with Raynaud's phenomenon. Total fingertip blood flow will be measured by venous occlusion air plethysmography; nutritive (capillary) blood flow will be determined by the disappearance rate of a radioisotope from a local depot injection in the fingertip. A-V shunt flow will be calculated by subtracting capillary from total blood flow. It is planned to study the effect of atropine, mental stress, tobacco smoking, and nicotine on a-v shunt and nutritive flow in normal subjects; only mental stress and tobacco smoking will be studied in patients with Raynaud's phenomenon. It is also planned to measure blood and plasma viscosity, using a cone viscometer, in a group of patients with Raynaud's disease and phenomenon due to secondary causes. If an abnormal viscosity is found, a therapeutic trial to lower it will be performed.